The present invention relates generally to chip-on-board module processing methods, and more particularly, to a top of die processing method that provides encapsulation on the top of a chip-on-board module in a manner that permits rework of the module and removal of integrated circuits used therein.
Encapsulation of wire bonded integrated circuits, commonly referred to as a "glob top" method for encapsulating chip-on-board modules, has been practiced in the electronics industry (primarily commercial) for many years to provide a form of environmental and mechanical protection for hybrids and multichip modules. Epoxy has proven to be a very effective barrier to moisture induced corrosion and damage resulting from physical handling. In the conventional glob top method, epoxy, or a similarly effective encapsulant, such as polyimide, for example, has traditionally been dispensed over the entire integrated circuit and over every portion of the wires that connect it to an underlying substrate.
However the integrated circuits that are encapsulated using the conventional glob top method are difficult or impossible to remove and replace. A typical glob topped die is not reworkable because epoxy is almost impossible to remove without ruining the underlying substrate and/or wire bond pads. The benefit of rework is especially important for today's multichip modules which are relatively expensive due to the complexity and cost of the integrated circuits and the substrate.
The present invention is similar to methods sometimes used in the electronics industry for tape automated bonding processes. Tape automated bonded devices are sometimes encapsulated on the surface of the device (including inner lead bonds) with epoxy or polyimide to provide environmental and mechanical protection, in addition to providing enhanced strength of the inner lead bonds. However, the approach provided by the present invention is not believed to have been used for wire bonded devices.
Accordingly, it is an objective of the present invention to provide for an improved top of die processing method that provides encapsulation on the top of a chip-on-board module in a manner that permits rework of the module and removal of integrated circuits used therein.